Ultra-trace level analysis, when applied to the testing of water, entails endeavouring to identify and measure the quantities of non-aqueous components of water, "analytes", that are present at levels of generally parts per billion or trillion, or less. Such analytes are either dissolved in water as molecules and ions are adsorbed on extraneous particulates and/or colloidal matter usually present in water or, in the case of organic micro-organisms, are in suspension. Thus, trace contaminants in water are distributed between dissolved and non-dissolved components.
This invention relates to analyzing the non-dissolved component of contaminants in fresh, or non-saline water. (Further reference to water herein is directed to non-saline water.) It also relates to analyzing dissolved components in certain cases where such components may be forced to precipitate from solution.
In general, the most toxic contaminants for chronic diseases present at ultra-trace levels in water are in the non-dissolved form. If a complete analysis of a water sample is required, the contaminants remaining in the permeate, principally those dissolved in the aqueous phase, may also be extracted by means of adsorption on a resin column following standard techniques. However, often it is sufficient to only analyze for the presence of the non-dissolved fraction.
To carry-out ultra-trace level analysis on water it is essential to sample sufficient volumes of water in order to collect a detectable quantity of contaminants. The cost of analysis increases when only smaller quantities of samples are available for testing. Therefore, the accumulation of large sample quantities will reduce costs and increase the number of techniques available to effect analysis. Accumulation of trace samples of micro-organisms will also allow identification through culturing samples to be effected more reliably.
Difficulties arise in applying most normal trapping techniques, such as filtration and adsorption, to the ultra-trace analysis of the non-dissolved components in surface or waste water. When suspended matter is present it is typical that only a relatively small volume of water can be made to flow readily through the normal sieve-type filter medium or the barrier-type filters used in ultra-trace filtration. This is because such filters have very fine pore dimensions, plug-up easily, and rapidly develop a high back-pressure. These are not convenient characteristics when it is intended to filter large volumes of water.
Depth-filters are less susceptible to blockage than barrier filters. Known depth-filters, on the other hand, are composed of random mats of polymeric materials and rely on the density and thickness of the mats to trap particles. These filters are generally capable of retaining larger quantities of particles within their matrices and this makes filtration of large volumes of fluids more practical. However, such filters are not efficient at trapping micron-level sized particles and colloids. Moreover, commercially available depth-filters usually contain contaminating binders that bleed during extraction of the analytes and thereby complicate analytical procedures.
Both sieve and depth filters of conventional design need to be of unwieldy size to be able to sample large volumes of turbid fluids.
Adsorption columns perform poorly as filters and have limited capacity to trap analytes. The consequence is that large volumes of adsorbers must be used if adsorption columns are to be used to collect significant quantities of analytes.
A further concern with adsorbers is that an extraction process is required to recover the analytes. The adsorber then contributes contaminants to the extract at levels which interfere with ultra-trace analysis. This inherent contamination problem persists in spite of extensive cleaning.
An unappreciated aspect of ultra-trace analysis as applied to fresh water is that many ultra-trace analytes have not been reliably quantified because they are entrained within metal hydroxyl colloids such as alumina silica colloids. Colloids create a problem in filters in that they readily block filter pores, thus limiting sample quantities. Consequently, to collect convenient quantities of colloidally-trapped analytes, large filter areas are required. Larger filters increase contamination.
In the case of adsorbers, while their poor recovery ratios have been recognized, there has apparently been little or no appreciation of the fact that adsorbers must compete with the binding capacity of colloids in order to accumulate trace analytes.
Accordingly, it is desirable to develop a compact form of a binder-free analytical trapping medium that will allow the extraction of ultra-trace level quantities of non-dissolved analytes found in non-saline water. Further, it is desirable to collect such analytes in concentrations that will make analysis convenient.
A further advantageous procedure when large volumes of water are being sampled, would be to limit the sampling time to only that required to produce a level of accumulated analytes susceptible to convenient detection.
It is on the basis of this background that the present invention is directed to improving the procedure by means of which ultra-trace analysis of large volumes of water may be carried-out.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with references to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention will then be further described, and defined, in each of the individual claims which conclude this Specification.